This invention relates to aqueous delivery of fluorinated silanes to a substrate. More particularly, the present invention is a dilutable, non-aqueous concentrate comprising at least one fluorinated silane and at least one fluorinated surfactant, which together with water or an aqueous solvent mixture form an aqueous dilution that may be coated and cured on a substrate.
Good oil-repellent and water-repellent coatings may be provided to certain substrates by applying to a substrate fluorinated silanes in the molten state or dissolved in volatile organic solvents. The applied fluorinated silanes are cured by heating with a catalyst to chemically affix the fluorinated silanes to the substrates. (See, for example, U.S. Pat. No. 3,012,006 (Holbrook et al.)). However, the use of volatile organic solvents is generally harmful to the environment, and may be hazardous due to the flammability of the solvents. Therefore, an alternative means to apply fluorinated silanes to substrates was developed, which is to use aqueous delivery. (See, for examples, U.S. Pat. No. 5,274,159 (Pellerite et al.), U.S. Pat. No. 5,702,509 (Pellerite et al.), and U.S. Pat. No. 5,550,184 (Halling)).
One problem with known compositions for the aqueous delivery of fluorinated silanes to substrates is that they may not have long shelf lives. Another problem is that they may require high-shear mixing before they are coated on a substrate. Known compositions have high solids content, which result in thick coatings
Although using aqueous delivery of fluorinated silanes to substrates is known in the art, there continues to be a desire to provide compositions for aqueous delivery of fluorinated silanes that: 1) can be stored for relatively long periods of time; 2) do not require high-shear mixing or other input of mechanical energy; 3) have relatively low solids content, making them easier to coat thinly on glass and other substrates; and 4) at the same time, once applied to a substrate and cured, can provide durable coatings.
The present invention provides compositions for the aqueous delivery of fluorinated silanes. One type of composition is a dilutable, non-aqueous concentrate and another type is an aqueous dilution comprising the dilutable, non-aqueous concentrate and a diluting medium that comprises water or an aqueous solvent mixture.
The dilutable, non-aqueous concentrate comprises a non-aqueous, homogeneous mixture comprising: (a) at least one fluorinated silane of the formula I:
Rf1xe2x80x94[xe2x80x94Qxe2x80x94[SiY3-xR1x]z]yxe2x80x83xe2x80x83(I)
wherein Rf1 represents a monofunctional or difunctional fluorinated group; Q independently represents an organic difunctional or trifunctional linking group; R1 independently represents a C1-C4 alkyl group; Y independently represents a hydrolyzable group; x is 0 or 1; y is 1 or 2; and z is 1 or 2; and (b) at least one fluorinated surfactant. The dilutable, non-aqueous concentrate may optionally further comprise one or both of at least one organic cosolvent and at least one additive.
The dilutable, non-aqueous concentrate must be diluted with water or an aqueous solvent mixture before being coated on a substrate. Advantageously, the dilutable, non-aqueous concentrate has a relatively long shelf life that is greater than about 1 day, preferably greater than about 14 days, and most preferably greater than about 6 months under proper storage conditions. The dilutable, non-aqueous concentrate may be shipped and stored more economically than in diluted form. The dilutable, non-aqueous concentrate may be diluted at the location where it is to be coated, which advantageously allows for greater flexibility in choices of the dilution and hence thickness of the coatings being applied. The dilutable, non-aqueous concentrate is dispersed in water or an aqueous solvent mixture (to form the aqueous dilution) simply by shaking by hand a mixture of the dilutable, non-aqueous concentrate and either water or an aqueous solvent mixture. No additional mechanical processing, such as high-shear mixing or ultrasonication, is required.
The aqueous dilution comprises: (a) a diluting medium comprising water or an aqueous solvent mixture comprising water and at least one water miscible cosolvent; and (b) a dilutable, non-aqueous concentrate comprising a non-aqueous, homogeneous mixture comprising: (i) at least one fluorinated silane of the formula I:
Rf1xe2x80x94[xe2x80x94Qxe2x80x94[SiY3-xR1x]z]yxe2x80x83xe2x80x83(I)
wherein Rf1 represents a monofunctional or difunctional fluorinated group; Q independently represents an organic difunctional or trifunctional linking group; R1 independently represents a C1-C4 alkyl group; Y independently represents a hydrolyzable group; x is 0 or 1; y is 1 or 2; and z is 1 or 2; and (ii) at least one fluorinated surfactant.
The aqueous dilution may be coated on a substrate to provide a durable coating. Advantageously, the aqueous dilution of the present invention has a relatively low solids content, which makes it easier to coat thinly on glass or other siliceous substrates that may have, for example, optical properties that are sensitive to thickness. The inventive aqueous dilution allows for the elimination of or the substantial reduction in the use of organic solvents in the process that may be flammable and/or harmful to the environment. The aqueous dilution also has a shelf life that is at least several hours under proper storage conditions.
Other embodiments of the present invention include a method of treating a substrate, and an article comprising a substrate and a coating that is formed by coating and curing the aqueous dilution.
The dilutable, non-aqueous concentrate of the present invention comprises a non-aqueous, homogeneous mixture that comprises at least one fluorinated silane and at least one fluorinated surfactant. The dilutable, non-aqueous concentrate may optionally further comprise at least one organic cosolvent, and/or at least one additive.
A xe2x80x9chomogeneous mixture,xe2x80x9d when referring to the dilutable, non-aqueous concentrate, is defined as the dilutable, non-aqueous concentrate being stable, i.e., no substantial precipitation or substantial phase separation occurs for at least the time necessary to prepare an aqueous dilution from the dilutable, non-aqueous concentrate, however, preferably, and for the purpose of being commercially practical, the dilutable concentrate is stable for a period of at least about one hour, and preferably up to about six months or longer, under proper storage conditions (closed container, no water, room temperature). The dilutable, non-aqueous concentrate may be clear or somewhat hazy.
By the term xe2x80x9cnon-aqueousxe2x80x9d it is meant that water is not added as a component of the dilutable, non-aqueous concentrate. However, there may be adventitious water in the other components of the composition, but the total amount of water does not adversely affect the shelf life or the stability of the dilutable, non-aqueous concentrate (i.e., preferably less than about 0.1 wt % of the dilutable, non-aqueous concentrate).
The fluorinated silane of the dilutable, non-aqueous concentrate has the formula
Rf1xe2x80x94[xe2x80x94Qxe2x80x94[SiY3-xR1x]z]yxe2x80x83xe2x80x83(I)
wherein Rf1 represents a monofunctional or difunctional fluorinated group, optionally containing one or more ether oxygen atoms, Q independently represents an organic difunctional or trifunctional linking group, R1 independently represents a C1-C4 alkyl group, Y independently represents a hydrolyzable group, x is 0 or 1, y is 1 or 2, and z is 1 or 2. Fluorinated silanes of Formula I are incompatible with water (meaning, the fluorinated silanes cannot substantially combine with water to form a single phase blend) and immiscible with water (meaning, the fluorinated silanes cannot substantially combine with water so as to result in the combination or blend exhibiting a single Tg or Tm).
The monofunctional or difunctional fluorinated group Rf1 includes linear, branched, and/or cyclic structures, that may be saturated or unsaturated. It is preferably a: perfluorinated group (i.e., all Cxe2x80x94H bonds are replaced by Cxe2x80x94F bonds). However, hydrogen or chlorine may be present as substituents instead of fluorine provided that not more than one atom of either is present for every two carbon atoms, and, preferably, if hydrogen and/or chlorine is present, the Rf1 group terminates in at least one perfluoromethyl group.
In one embodiment, Rf1 includes mono- and/or difunctional perfluoropolyethers comprising perfluorinated repeating units selected from the group consisting of xe2x80x94(CnF2n)xe2x80x94, xe2x80x94(CnF2nO)xe2x80x94, xe2x80x94(CF(Z))xe2x80x94, (CF(Z)O)xe2x80x94, xe2x80x94(CF(Z)CnF2nO)xe2x80x94, xe2x80x94(CnF2nCF(Z)O)xe2x80x94, and combinations thereof. In these repeating units, Z is a fluorine atom, a perfluoroalkyl group, an oxygen-substituted perfluoroalkyl group, a perfluoroalkoxy group, or an oxygen-substituted perfluoroalkoxy group, all of which can be linear, branched, or cyclic, and preferably have about 1 to about 9 carbon atoms and 0 to about 4 oxygen atoms. Examples of perfluoropolyethers containing polymeric moieties made of these repeating units are disclosed in U.S. Pat. No. 6,277,485 (Invie et al.) (which is incorporated herein by reference). For the monofunctional perfluoropolyether group, the terminal groups can be (CnF2n+1)xe2x80x94, (CnF2n+1O)xe2x80x94 or (Xxe2x80x2CnF2nO)xe2x80x94, wherein Xxe2x80x2 is H, Cl, or Br, for example. Preferably, these terminal groups are perfluorinated. In these repeating units or terminal groups, n is 1 to 6, and preferably 1 to 3.
Preferred approximate average structures for a difunctional perfluoropolyether group include xe2x80x94CF2O(CF2O)m(C2F4O)pCF2xe2x80x94; xe2x80x94CF(CF3)(OCF2CF(CF3))mO(CnF2n)O(CF(CF3)CF2O)pCF(CF3)xe2x80x94, n ranges from 2 to 4; xe2x80x94CF2O(C2F4O)pCF2; and xe2x80x94(CF2)3O(C4F8O)p(CF2)3xe2x80x94; wherein average values for m and p range from 0 to 50, with the proviso that m and p are not simultaneously zero. Of these, particularly preferred approximate average structures are xe2x80x94CF2O(CF2O)m(C2F4O)pCF2xe2x80x94, xe2x80x94CF2O(C2F4O)pCF2xe2x80x94, and xe2x80x94CF(CF3)(OCF2CF(CF3))mO(CnF2n)O(CF(CF3)CF2O)pCF(CF3)xe2x80x94, wherein n ranges from 2 to 4 and the average value of m+p is from about 4 to about 20.
Particularly preferred approximate average structures for a monofunctional perfluoropolyether group include C3F7O(CF(CF3)CF2O)pCF(CF3)xe2x80x94 and CF3O(C2F4O)pCF3xe2x80x94 wherein an average value for p is 4 to 50. As synthesized, these compounds typically include a distribution of oligomers and/or polymers, so p and m may be non-integral. The approximate average structure is the approximate average over this distribution.
These distributions may also contain perfluorinated chains having no functional groups (inert fluids) or more than two terminal groups (branched structures) as a consequence of the methods used in their synthesis. Typically, distributions containing less than about 10% by weight of nonfunctionalized compounds (e.g., those without silane groups) can be used.
Throughout, when referring to the distributions (m, n, and p), the words xe2x80x9caverage value of p,xe2x80x9d for example, may be used interchangeably with the words xe2x80x9caverage value for p,xe2x80x9d xe2x80x9cnumber average p,xe2x80x9d and the symbols xe2x80x9cPavgxe2x80x9d and xe2x80x9cPav.xe2x80x9d The different ways of referring to the distribution mean the same thing, as described above.
In another embodiment Rf1 includes mono- and difunctional perfluoroalkyl and perfluoroalkylene groups of the respective formulas CnF2n+1xe2x80x94 and xe2x80x94CnF2nxe2x80x94, where n is 3 to 20, preferably 4 to 10. Such groups may be linear or branched, or a mixture thereof.
Suitable linking groups, Q, include difunctional or trifunctional organic linking groups optionally containing heteroatoms (such as sulfur, oxygen, nitrogen, and the like, for examples) and/or functional groups (such as amides, esters, sulfonamides, carbonates, and the like, for examples).
Examples of Q groups include, but are not limited to, difunctional groups: xe2x80x94C(O)NH(CkH2k)xe2x80x94, xe2x80x94SO2NR(CkH2k)xe2x80x94, xe2x80x94(CkH2k)xe2x80x94, xe2x80x94CH2O(CkH2k)xe2x80x94, xe2x80x94C(O)S(CkH2k)xe2x80x94, and xe2x80x94CH2OC(O)N(R)(CkH2k)xe2x80x94, wherein R is hydrogen or a C1-C4 alkyl group, and wherein k is 2 to 25; and the trifunctional group: 
Preferred linking groups (Q) are xe2x80x94C(O)NH(CH2)3xe2x80x94, xe2x80x94CH2O(CH2)3xe2x80x94, and xe2x80x94CH2OC(O)N(R)(CH2)3xe2x80x94, when Rf1 is a perfluoropolyether. Other preferred linking groups (Q) are xe2x80x94SO2NR(CkH2k)xe2x80x94, xe2x80x94CkH2kxe2x80x94 where k is greater than or equal to 2, and xe2x80x94CH2O(CH2)3xe2x80x94, when Rf1 is a perfluoroalkyl or perfluoroalkylene.
Y independently represents a hydrolyzable group in Formula I. Specific preferred examples of hydrolyzable groups include methoxy groups, ethoxy groups, C3-C6 alkoxy groups optionally containing one ether oxygen, and mixtures thereof. If there is more than one type of Y in the fluorinated silane, each Y is a hydrolyzable group, but they need not be the same hydrolyzable group.
R1 independently represents a C1-C4 alkyl group. Examples of alkyl groups that are preferred include methyl and ethyl groups.
Fluorinated silanes of Formula I generally have a molecular weight (number average) of at least about 300 grams per mole, and preferably, at least about 500 grams per mole, and most preferably between at least about 1000 grams per mole and 3000 grams per mole.
With respect to Formula I, a preferred group of fluorinated silanes includes those where:
Rf1 is:
(a) xe2x80x94CF(CF3)(OCF2CF(CF3))mO(CnF2n)O(CF(CF3)CF2O)pCF(CF3)xe2x80x94, wherein average values of m and p are from 1 to 20, m+pxe2x89xa620, more preferably m+p=about 4 to about 12, and n ranges from 1 to 4; or
(b) xe2x80x94CF2O(CF2O)m(CF2CF2O)pCF2xe2x80x94, and the average value of m+p=16 to 24;
(c) C3F7O(CF(CF3)CF2O)pCF(CF3)xe2x80x94, wherein the average value of p=4 to 15;
(d) CF3O(CF2CF2O)pCF2xe2x80x94, wherein the average value of p=5 to 20; or
(e) CF3CF2CF2O(CF2CF2CF2O)nxe2x80x94, wherein navg=1 to 20.
Q is independently an organic difunctional or trifunctional linking group, optionally containing a heteroatom or a functional group;
R1 is independently a C1-C4 alkyl group;
Y is independently selected from the group consisting of methoxy groups, ethoxy groups, C3-C6 alkoxy groups optionally containing one ether oxygen, and mixtures thereof;
x is 0 or 1;
y is 1 or 2; and
z is 1 or 2.
When Rf1 is a perfluoroalkyl or perfluoroalkylene group, Rf1 may include linear, branched, or cyclic structures, that may be saturated or unsaturated. Rf1 may be represented by the formulae xe2x80x94Ckxe2x80x2F2kxe2x80x2+1 for a perfluoroalkyl group, or by xe2x80x94Ckxe2x80x2F2kxe2x80x2xe2x80x94 for a perfluoroalkylene group, wherein kxe2x80x2 is about 3 to about 20, more preferably, about 6 to about 12, and most preferably, about 7 to about 10. With reference to Formula I, the difunctional or trifunctional Q group may comprise linear, branched, or cyclic structures, that may be saturated or unsaturated.
Typically, suitable fluorinated silanes include a mixture of isomers (e.g., a mixture of compounds containing linear and branched perfluoroalkyl groups). Mixtures of fluorinated silanes exhibiting different values of kxe2x80x2 can also be used.
Examples of preferred fluorinated perfluoroalkylsilanes include, but are not limited to, the following: C7F15CH2OCH2CH2CH2Si(OCH3)3; C7F15CH2OCH2CH2CH2Si(CH3)(OCH3)2; C7F15CH2OCH2CH2CH2Si(OC2H5)3; C8F17SO2N(Et)CH2CH2CH2Si(OCH3)3; C4F9SO2N(Me)CH2CH2CH2Si(OCH3)3; C8F17CH2CH2Si(OCH3)3; C3F7CH2OCH2CH2CH2Si(OCH3)3)3; C6F13CH2CH2Si(OCH2CH3)3; and C8F17CH2CH2Si(OCH2CH3)3. Mixtures of these fluorinated perfluoroalkyl silanes may be used if desired.
The fluorinated silanes of Formula I can be synthesized using standard techniques. For example, commercially available or readily synthesized perfluoropolyether esters can be combined with a functionalized silane, such as a 3-aminopropyltrisilane, according to methods taught in U.S. Pat. No. 3,810, 874 (Mitsch et al.) and U.S. Pat. No. 3,646,085 (Bartlett), which are incorporated herein by reference. These materials may or may not need to be purified before use in the dilutable, non-aqueous concentrate.
The fluorinated silane is generally included in the dilutable, non-aqueous concentrate composition in an amount between about 10 wt % and about 80 wt % of the dilutable, non-aqueous concentrate, preferably between about 20 wt % and about 75 wt %, and most preferably between about 25 wt % and about 50 wt %.
A surfactant is defined as xe2x80x9ca substance that, when present at low concentration in a system, has the property of adsorbing onto the surfaces or interfaces of the system and of altering to a marked degree the surface or interfacial free energies of these surfaces.xe2x80x9d (Milton J. Rosen, xe2x80x9cSurfactants and Interfacial Phenomena,xe2x80x9d Second Ed., John Wiley and Sons, New York, NY, 1989, page 1). These surfactants have xe2x80x9ca characteristic molecular structure consisting of a structural group that has very little attraction for [a] solvent, known as a lyophobic group, together with a group that has a strong attraction for [a] solvent, called the lyophilic group . . . .xe2x80x9d (Milton J. Rosen, xe2x80x9cSurfactants and Interfacial Phenomena,xe2x80x9d Second Ed., John Wiley and Sons, New York, N.Y., 1989, pages 3-4). When the solvent is aqueous, the lyophobic group is typically a nonpolar group such as alkyl or fluorinated alkyl, while the lyophilic group is a polar group.
The term xe2x80x9cfluorinatedxe2x80x9d (as in the term fluorinated surfactant) indicates that at least about 75 percent, preferably at least about 85 percent, more preferably at least about 95 percent, of the hydrogen atoms of the alkyl moiety are replaced by fluorine atoms. Optionally, remaining hydrogen atoms can be replaced by other halogen atoms, such as by chlorine atoms.
The fluorinated surfactant acts to stabilize an emulsion (that is, droplets of one liquid phase dispersed in another liquid phase), and can aid in solubility or compatibility of the fluorinated silane(s) and the organic cosolvent(s) (if there is one or more organic cosolvent(s)) of the dilutable, non-aqueous concentrate.
Fluorinated surfactants useful in this invention are amphiphilic materials, comprising one or more hydrophobic fluorochemical segments and one or more solubilizing and hydrophilic segments. Such materials are described in xe2x80x9cFluorinated Surfactants and Repellentsxe2x80x9d, Second Edition, by E. Kissa, Surfactant Science Series, Volume 97, Marcel Dekker, Inc.: New York, 2001, pp 1-21. The fluorinated surfactants have a fluorine content by weight of at least 10%. These fluorinated surfactants can be monomeric or polymeric, with molecular weights between about 300 and about 100,000 grams per mole, preferably between about 400 and about 20,000 grams per mole. The hydrophobic fluorochemical groups can be, for instance, perfluoroalkyl containing between about 3 and about 20 carbon atoms, or a mono- or divalent perfluoropolyether group with molecular weight between about 300 and about 10,000 grams per mole. Hydrophilic groups on the fluorinated surfactants can be of anionic (such as carboxylate), cationic (such as quaternary ammonium), nonionic (such as oligo(oxyethylene)) or amphoteric (such as amine oxide) nature as long as they do not contain functionalities that cause instability in the concentrates of this invention, for example strongly acidic groups, strongly basic groups, or contamination by fluoride ions.
Representative fluorinated surfactants include, but are not limited to, the following:
C7F15CO2xe2x88x92NH4+
C8F17SO2N(C2H5)(C2H4O)7CH3 
C8F17(C2H4O)10H
(C4F9SO2)2N31 NH4+
C4F9SO2N(CH3)(C2H4O)nCH3 (where navgxcx9c7)
C3F7O(CF(CF3)CF2O)nCF(CF3)CO2xe2x88x92NH4+ (where navgxcx9c13)
Examples of these and other fluorinated surfactants of the present invention are described, for example, in U.S. Pat. No. 3,772,195 (Francen), U.S. Pat. No. 4,090,967 (Falk), U.S. Pat. No. 4,099,574 (Cooper et al.), U.S. Pat. No. 4,242,516 (Mueller), U.S. Pat. No. 4,359,096 (Berger), U.S. Pat. No. 4,383,929 (Bertocchio et al.), U.S. Pat. No. 4,472,286 (Falk), U.S. Pat. No. 4,536,298 (Kamei et al.), U.S. Pat. No. 4,795,764 (Alm et al.), U.S. Pat. No. 4,983,769 (Bertocchio et al.) and U.S. Pat. No. 5,085,786 (Alm et al.), which are herein incorporated by reference. Many of these fluorinated surfactants are commercially available from Minnesota Mining and Manufacturing Company (St. Paul, Minn.), having the tradename FLUORAD(trademark), or commercially available from E.I. DuPont de Nemours and Co. (Wilmington, Del.), having the tradename ZONYL(trademark).
Polymeric fluorinated surfactants can also be used in the present invention. Examples of polymeric fluorinated surfactants that may be used in the present invention are found in U.S. Pat. No. 3,787,351 (Olson), U.S. Pat. No. 4,668,406 (Chang), and PCT Intl""l App. WO 01/30873, which are incorporated herein by reference.
Examples of polymeric fluorinated surfactants that may be used include random copolymer fluorinated surfactants. Examples of random copolymer fluorinated surfactants include the following structures: 
wherein the molar ratio of a:b:c is about 30: about 1 : about 32, and wherein the molecular weight of the surfactant is about 1,000 to about 4,000 grams per mole; and 
wherein the molar ratio of axe2x80x2:bxe2x80x2:cxe2x80x2 is about 3: about 3: about 1, and wherein the molecular weight of the surfactant is about 5,000 to about 40,000 grams per mole.
The fluorinated surfactant is generally included in the dilutable, non-aqueous concentrate in an amount up to about 50 wt % of the dilutable, non-aqueous concentrate, preferably up to about 30 wt %, and most preferably up to about 15 wt %.
A dilutable, non-aqueous concentrate of the present invention may also optionally include one or more organic cosolvents. An organic cosolvent is an organic liquid component that renders the surfactant(s) and the fluorinated silane(s) compatible (in case they are not compatible in the absence of the organic cosolvent), and lowers the viscosity of the dilutable, non-aqueous concentrate.
Suitable organic cosolvents are organic solvents, or mixtures of organic solvents, that include, but are not limited to, aliphatic alcohols, such as methanol, ethanol, and isopropyl alcohol; ketones, such as acetone or methyl ethyl ketone; esters, such as ethyl acetate or methyl formate; ethers, such as diisopropyl ether, 1,4-dioxane, and diethylene glycol dimethyl ether; and amides, such as N-methylpyrrolidinone, and N, N-dimethylformamide. Fluorinated organic solvents, such as heptafluorobutanol, trifluoroethanol and hexafluoroisopropanol, may be used alone or in combination with non-fluorinated organic cosolvents.
Preferred organic cosolvents are aliphatic alcohols. Some examples of preferred aliphatic alcohols are ethanol, methanol and isopropyl alcohol. Other examples include DOWANOL(trademark) PnP (available from Sigma-Aldrich, Milwaukee, Wis.), and DOWANOL(trademark) PM (available from Sigma-Aldrich), etc.
Preferably, the organic cosolvent is water miscible. Also, preferably, the organic cosolvent has a boiling point that is below 200xc2x0 C.
The organic cosolvent may generally be included, if used, in the dilutable, non-aqueous concentrate in an amount up to about 75 wt % of the dilutable, non-aqueous concentrate, and preferably up to about 50 wt %.
The dilutable, non-aqueous concentrate may also include one or more optional additives.
Some examples of optional additives are catalysts to assist with curing and/or crosslinking of the dilutable, non-aqueous concentrate once it is diluted and coated on a substrate. A curing additive may be added when necessary to facilitate the cure. Such a curing additive may take the form of an acid precursor, which releases an acid upon exposure to heat, ultraviolet light, visible light, electron beam irradiation, or microwave irradiation. Acid precursors include, for instance, sulfonium and iodonium salts as well as alkyl esters of alkane- or fluoroalkanesulfonic acids, and are described in U.S. Pat. No. 6,204,350 (Liu et al.) incorporated by reference.
Some additives, such as ammonium salts of acids such as perfluorocarboxylic acids, alkylsulfonic acids, arylsulfonic acids, perfluoroalkylsulfonic acids, and perfluoroalkylsulfonimides can function as latent or thermally activated curing additives as well as function as surfactants. Therefore, the dilutable, non-aqueous concentrate may include one of these dual-functioning surfactants, and may not need a separate catalyst.
Other possible optional additives include, but are not limited to, hydrocarbon surfactants, silicone surfactants, antimicrobial agents, UV absorbers, hydrocarbon silanes, and micro- or nanoparticles of inorganic materials, such as silica or titania.
An optional additive or additives may be included in the dilutable, non-aqueous concentrate in an amount up to about 50% by weight of the dilutable, non-aqueous concentrate, more preferably up to about 5% by weight.
The dilutable, non-aqueous concentrate may be prepared by combining the components in any order and in a fashion that is known in the art. Preferably, for the embodiment comprising at least one fluorinated silane, at least one fluorinated surfactant and at least one organic cosolvent, the surfactant(s) and organic cosolvent(s) are first mixed and then the fluorinated silane(s) is added to the mixture.
If the dilutable, non-aqueous concentrate is not immediately homogeneous after mixing the ingredients, the concentrate may become homogeneous after time has passed. In order to speed homogeneity, however, the dilutable, non-aqueous concentrate may be heated.
For ease of manufacture etc., the dilutable, non-aqueous concentrate is typically diluted with a diluting medium (or the aqueous dilution composition is typically prepared) shortly before use.
The presence of certain chemical functionalities such as strong acids (i.e., sulfonic, mineral, phosphoric, and perfluorinated acids) and species such as fluoride ion are preferably avoided in the dilutable, non-aqueous concentrate of this invention if they lead to instability of the corresponding aqueous dilution and/or the dilutable, non-aqueous concentrate itself.
Another embodiment of the present invention is an aqueous dilution, which comprises: the dilutable, non-aqueous concentrate, described above; and, a diluting medium that comprises water or an aqueous solvent mixture comprising water and a water miscible cosolvent. The aqueous dilution may also include optional additives.
The diluting medium of the aqueous dilution comprises water or an aqueous solvent mixture. The aqueous solvent mixture comprises water and a water miscible cosolvent.
Examples of water miscible cosolvents include, but are not limited to, methanol, ethanol, isopropyl alcohol, acetone, diethylene glycol dimethyl ether, DOWANOL(trademark) PM, and N-methylpyrrolidinone.
The amount of water miscible cosolvent that is included in the aqueous dilution (if an aqueous solvent mixture is used) is dependent upon the coating technique that is to be used to coat the aqueous dilution, as well as dependent upon the performance characteristics that are desired in the resultant coated substrate.
The aqueous dilution may also optionally comprise at least one additive. Some exemplary additives are described above. The optional additive(s) of the aqueous dilution may be in addition to the additive(s) in the dilutable, non-aqueous concentrate. As discussed above with regard to the dilutable, non-aqueous concentrates, additives which adversely affect the stability of the aqueous dilution are preferably avoided. These additives may include strongly acidic species and fluoride ions. The pH of the aqueous dilution is in the range of about 2 to about 11, and most preferably about 4 to about 8.
The aqueous dilution may be prepared by first combining the components of the dilutable, non-aqueous concentrate and then subsequently adding the dilutable, non-aqueous concentrate to the diluting medium. The aqueous dilution is preferably prepared, however, by adding the diluting medium to the dilutable, non-aqueous concentrate.
The amount of dilutable, non-aqueous concentrate that is typically in the aqueous dilution is from about 0.05 wt % to about 10 wt % of the aqueous dilution, preferably from about 0.1 wt % to about 2 wt %. The aqueous dilution may be a clear solution as well as a somewhat hazy solution.
An optional additive or additives may be added to the aqueous dilution after the dilutable, non-aqueous concentrate has been diluted. One preferred optional additive is a curing additive, such as those discussed above, that may be added to the aqueous dilution in an amount up to about 3 wt % of the aqueous dilution.
The aqueous dilution is generally applied to a substrate (substrate described in detail below with regard to the method) in an amount sufficient to produce a coating that is water and oil repellent. This coating can be extremely thin, e.g., about 1 to about 2 nanometers in thickness, though in practice a coating may be thicker, e.g., up to about 50 nanometers in thickness.
Alternatively, a substrate may be first treated with the aqueous dilution, and then treated with acid to promote curing of the silane. The acid may be applied neat, but is preferably applied as a solution in water or in an organic solvent.
The aqueous dilution of the present invention advantageously spreads well on a substrate to achieve uniform properties over the whole surface of the treated substrate. In addition, the aqueous dilutions minimize or eliminate the use of volatile organic compounds (VOCs), thereby reducing pollution and exposure to potentially harmful, and often flammable, solvent vapors.
The present invention also provides a method for treating a substrate, comprising the steps of applying the aqueous dilution of the invention, as discussed above, to a substrate and curing the aqueous dilution to form a treated substrate.
Suitable substrates that can be treated with the aqueous dilution of this invention include, but are not limited to, substrates having a hard surface preferably with functional groups, such as xe2x80x94OH groups that occur on siliceous substrates, capable of reacting with the silane. Preferably, such reactivity of the surface of the substrate is provided by functional groups having active hydrogen atoms, such as xe2x80x94OH. When such active hydrogen atoms are not present, the substrate may first be treated in a plasma containing oxygen or in a corona atmosphere to make it reactive to the fluorinated silane.
Treatment of substrates renders the treated surfaces less retentive for soils and more readily cleanable due to the oil and water repellent nature of the treated surfaces. These desirable properties are maintained despite extended exposure or use and repeated cleanings because of the high degree of durability of the treated surface.
Preferably, the substrate is cleaned prior to applying the aqueous dilution of the present invention so as to obtain optimum characteristics, particularly durability. That is, the surface of the substrate to be coated preferably is substantially free of organic contamination prior to coating. Cleaning techniques depend on the type of substrate and include, for example, a solvent washing step with an organic solvent, such as acetone or ethanol, or exposure to a reactive gas-phase treatment such as air plasma or UV/ozone.
Useful substrates include, but are not limited to, textiles, apparel, leather, paper, cardboard, carpet, ceramics, glazed ceramics, porcelain, flat glass, hollow glass, metals (such as aluminum, iron, stainless steel, copper and the like), metal oxides, natural and man-made stone, thermoplastic materials (such as poly(meth)acrylate, polycarbonate, vinyl, polystyrene, styrene copolymers such as styrene/acrylonitrile copolymers, and polyesters such as polyethylene terephthalate), paints (such as those based on acrylic resins), powder coatings (such as polyurethane, epoxy or hybrid powder coatings), and wood.
Preferred substrates include metals and siliceous substrates including ceramics, glazed ceramics, glass, concrete, mortar, grout and natural and man-made stone. Particularly preferred substrates include glazed ceramics and glass. Various articles, having at least one substrate, can be effectively treated with the inventive aqueous dilution to provide a water and oil repellent coating thereon. Examples include glazed ceramic tiles, enameled bathtubs or toilets, glass shower panels, construction glass, various parts of a vehicle (such as the mirror or windscreen), and glazed ceramic or enamel pottery materials.
Another particularly preferred substrate is a substrate having an antireflective (AR) film on it. Antireflective (AR) films prepared by vacuum sputtering of metal oxide thin films on substrates made of glass or plastic are particularly useful in display devices of electronic equipment. Such metal oxide films are relatively porous and consist of clusters of particles forming a relatively rough profile. AR films help reduce glare and reflection. When the AR films are conductive, they also help reduce static discharge and electromagnetic emissions. Thus, a primary application for AR films is to provide contrast enhancement and antireflective properties to improve the readability of display devices, such as computer monitors. AR films are described in U.S. Pat. No. 5,851,674 (Pellerite et al.), which is incorporated herein by reference.
Sputtered metal oxide antireflective films are generally durable and uniform. Also, their optical properties are controllable, which makes them very desirable. They also have very high surface energies and refractive indices. However, the high surface energy of a sputtered metal oxide surface makes it prone to contamination by organic impurities (such as skin oils). The presence of surface contaminants results in a major degradation of antireflectivity properties of the metal oxide coatings. Furthermore, because of the high refractive indices, surface contamination becomes noticeable to the end-user. The present inventive method allows for a protective coating on an antireflective film that is relatively durable, and more resistant to contamination and easier to clean than the antireflective film by itself.
Preferably, the overall coating thickness of the dried coating (xe2x80x9cdried down coatingxe2x80x9d) of the aqueous dilution on an antireflective article is greater than a monolayer (which is typically greater than about 1.5 nanometers (nm) thick). That is, preferably, a coating from the aqueous dilution is at least about 2.0 nm thick for antisoiling purposes on articles having an AR film, and more preferably, at least about 3.0 nm thick. Preferably, it is less than about 10.0 nm thick, and more preferably, less than about 5.0 nm thick. The coating from the aqueous dilution is typically present in an amount that does not substantially change the antireflective characteristics of the antireflective article.
Methods for applying the aqueous dilution to a substrate include, but are not i limited to, spray, spin, dip, flow, and roll coat methods, etc. A preferred coating method: for application of the aqueous dilution includes spray application. Spraying may be effected by passing the pressurized aqueous dilution though a suitable jet, nozzle or orifice onto the substrate surface in the form of a stream or atomized mist.
A substrate to be coated can typically be contacted with the aqueous dilution at room temperature (typically about 20xc2x0 C. to about 25xc2x0 C.). Alternatively, the aqueous dilution can be applied to a substrate that is preheated at a temperature of, for example, between 60xc2x0 C. and 150xc2x0 C. This is of particular interest for industrial production, where e.g., ceramic tiles can be treated immediately after the firing oven at the end of the production line. Following application, the treated substrate can be dried and cured at ambient or elevated temperature for a time sufficient to dry or cure.
The obtained coating on the substrate may be cured by UV radiation or thermally. For UV cure, curing additives may be added (such as those optional additives described above). Thermal curing is performed at an elevated temperature of about 40 to about 300xc2x0 C., although elevated temperatures may not be required. The heat for curing can be supplied either through an initial preheat of substrates having sufficient heat capacity to provide the heat for curing, or through heating of coated substrates by an external heat source subsequent to coating.
Another embodiment of the present invention is an article comprising: (a) a substrate (as described above); and, (b) a coating on said substrate obtained by applying the aqueous dilution (described above) onto said substrate and curing said aqueous dilution.